Woodrow Wilson was so incapacitated by a series of strokes that his wife, Edith, became the virtual acting president. Franklin Roosevelt died of a massive stroke on April 12, 1945, leaving the presidency to an unprepared Harry Truman just as World War II was ending. And in 2000, former President Gerald Ford began slurring his words during a TV interview.

"Strokes affect the brain. And everything we do -- from simple motor functions to more complex behaviors such as planning, reasoning and judgment -- is brain-related," Biller said. "When a stroke affects a president, it can have a major impact not only on the individual, but on the world."

Biller is co-author of a study, titled "Stroke and the American Presidency," in the Journal of Stroke and Cerebrovascular Diseases. Since the article's publication in 1997, Biller has continued to observe from afar the neurological health of presidents and other major political figures. Biller is chair of the Department of Neurology at Loyola University Chicago Stritch School of Medicine.

Biller said the afflicted presidents had several stroke risk factors in common. Being men, they were more likely than women to suffer strokes. Seven of the 10 presidents were older than 65 when they suffered strokes. And, of course, the presidency is an extremely stressful job.

Plus, some of the presidents who suffered strokes had unhealthy lifestyles. Chester Arthur was obese and got little exercise. Franklin Roosevelt was a heavy smoker. Andrew Johnson may have abused alcohol. Wilson and Dwight Eisenhower suffered nonfatal strokes while in office. (Unlike Wilson, Ike did not suffer serious disabilities).

What happens if a president suffers a debilitating stroke while in office? The 25th Amendment to the Constitution provides a mechanism for the vice president to become acting president should the president be unable to perform his or her duties.

Stroke treatments have significantly improved in recent years. And the sooner a patient arrives at the hospital, the better the outcome, Biller said.